A conventional plasma processing apparatus for performing a plasma process such as an etching process on an object, e.g., a semiconductor wafer, to be processed, detects intensities of lights emitted from a plasma generated during the etching process, thereby monitoring an operating status of the apparatus or a processing status of the processed object. For example, there is disclosed a technique for monitoring the processing status of the object being processed, e.g., an end point detection of etching (see, e.g., Japanese Patent Laid-Open Publication No. H5-29276).
Such technique monitors emission intensities of activated species of process gas and reaction product emitted during a plasma process, to thereby detect the end point of the etching based on a ratio of the luminous intensities of two wavelengths. In other words, when the etching is completed due to the depletion of objects to be etched, the amount of activated species of process gas that contributes to the reaction starts increasing, and so does the emission intensity of the activated species of process gas. In contrast, since the amount of reaction products is comparatively reduced, the emission intensity thereof is also decreased. Based thereon, changes in the ratio of the emission intensity of process gas to that of reaction product are detected, thereby enabling an accurate end point detection of the etching.
Recently, as semiconductor devices becomes more compact, holes formed in a semiconductor wafer, for example, are also required to have a smaller opening ratio. However, monitoring the changes in the emission intensities of only two wavelengths of the activated species of process gas and the reaction products as described above is not sufficient to improve the accuracy of detecting the processing status, e.g., the end point detection of the etching.
Further, in case a noise is mixed in a sensor for detecting changes in the emission intensities of wavelengths in plasma, it is difficult to accurately detect the end point of the etching and estimate whether or not the plasma is stable in a processing chamber of the plasma processing apparatus, thereby deteriorating the accuracy of estimating a processing status of an object being processed or an operating status of a semiconductor manufacturing apparatus.